This invention relates generally to improvements to variable inlet guide vanes in axial flow compressors of the type used in industrial gas turbines. More particularly, the invention relates to improved constructions for reducing or suppressing vibratory response in variable inlet guide vanes which are caused by aerodynamic forces on the vanes at different rotated positions, particularly when the vanes are in the open position.
Axial flow compressors used in industrial gas turbines, often employ stationary radial vanes which may be rotated in unison to vary the angles of the vanes with respect to the fluid flowing through an annular passage in the frame of the compressor. The vanes are often rotatably mounted on radial spindles which support the outer part of the vanes. However, the inner tips of the vanes are subject to deflection and vibratory response, which varies with the turbulent conditions of fluid flow and with the position of the vanes.
One approach in the prior art to suppressing vibratory response in variable inlet guide vanes of axial flow compressors has been to limit the vane tip motion. A known partial solution to this problem is by means of a cylindrical radially projecting button at the vane's inner diameter that fits within a bushing supported in the stator frame. By limiting clearance between vane button and bushing, tip motion is limited. Vibration amplitude is controlled by selecting the clearance of the button within the bushing. However, some clearance must be provided to allow the vane to rotate through its closed-to-open position without binding.
When the vanes are in the closed position, i.e. providing maximum turning of the inlet air flow, the aerodynamic forces of the fluid on the vane are relatively great and deflect the vane so that the button contacts the bushing wall and suppresses vibration. However, when the inlet guide vanes are in the open position, with minimum turning of the inlet air, the aerodynamic forces on the vane are much smaller and the button is sometimes free to vibrate within the clearance of the bushing. This can lead to fatigue failure of the vane.
Accordingly, one object of the present invention is to provide an improved construction for suppressing vibratory response of variable inlet guide vanes in axial flow compressors.
Another object of the invention is to provide an improved construction for variable inlet guide vanes which reduces vibratory response in the open position when aerodynamic forces are at a minimum.